Electric discharge device



Sept. 30, 1952 H. C.'STEI NER 2,612,613

ELECTRIC DISCHARGE DEVICE Filed Feb. 25, 1950 O0 0 o o 00 o o JInventor":

Harry CSteiner,

by/flnzsz. 0 M

. His Attorney.

Patented Sept. 30, 1952 ELECIRIC; DISCHARGE: neuron Harry G. Steiner,Scotia, N, Y;, assignor to General Electric Company, a'corppration of-New- York-- Applica ion February 25, 1950, Serial No. 146,175}.

6 Claims.

My, I invention relates to. electric discharge devices and has. specialreferenceto, devices of the typewhich employes. a. pool-type, cathode,such as .a cathode constituted of mercury.

Control electrodes, or grids as. they are. commonlyrcalled, have beenemployed-in electric discharge. deviceshavin pool-type. cathodes toelectnQStaticaHy. control the starting; of the anode current-in eachloadcycle. Single-anode devices oi this typenhave; found wide andsuccessful use, particularly in industrial applications, as in rec.-t-ifieation. and" inversion,,. where. the very high emission -capacityof :the mercury. pool commonly employed as the cathode meetsheavy..duty. and short-circuit current. requirements. Arc backs arestill alimiting condition.ln-theusualinstallation of-zsuchdevices-;.-and hence provision must be made, tor rapid'deionization ofthe-arc plasma at the-"beginning; of an inverse cycle whenthe device,anode is: ne ative. in potential with respect tonthe-acathode;

*Wh-ile. theogrid,aperturesmay be made relatively small inorderthatagreater degree of control beexercised-both during theload and inversecycles, especially: at. high temperatures, the grid openings musthesufiiciently, large. to pass the maximum currents. required.Accordingly, the usual'method of hastening deionization-.means for.cooling :the. are plasmafiecannot. be neglected, and; so,-. devices orthis type: are usually encased in-a zwaterjacketedelongated metalliccylinder at cathode potential, which discharges thefiions and condensesthecathodevapor. At the samev time, itsis desirable tobeable toinitiatethe conduc tion cycle. when-the-device is at low. temperatureswithout, providing, preheating means or. using excessive.anode-"voltages...

finch-difficulty in starting devices of lthis nature ooours-duetolack ofionization at. thelow cathode vapor pressure'prevailing when the tube iscold. 'Whenthe ambient tem peratureis very low the. internal vaporpressurebefore. operation approaches; that-. degree of vacuum associatedwith conventional vacuum tubes and the .mean

freepath of the-ions necessary toestablish' conduction-is relativelylong. The passage. through the grid. openings; maybe-so.- constrictedthat the cathodevapordifiusestoo slowly up through, the gridtoreplenishtheion supply. Even .at highly positiveanode potentialsrelatively fewelectrons reach the. anode, although an .arc may be estabe lishedbetweenthe .grid. and cathode; spot.

This proble'ni is, amplified as the-current rating, and. hence, the size o f;,- the device, is.- increased, due-yto. the usually longer arepath. and the increased difiiculty of deionization;

x111 18.38112 object 0flmy;:in'vention to provide a pooltype; cathodedischargezadevice of the nature desoribed'in"whichr conduction may beeasily established: at low temperatures. ti I be. best. iunderstood;.b-y re erenc to It is another, object of my invention toprqvifde an improved discharge device" ofthe. nature describedfwhiohmaybe successfully operated ovei' awide, rangeofvapor pressures; I g

My, nventio i ad tag u c porated in an electric, discharge device-oithetype h-aving a pool-:tyhe. Cathode. and a'd'eionizii'1g"meta11lcenvelope surface surroundingithe discharge path; A control electrode orgridf'having'a bottomd-i 'sk' liken rti n extendi t nsv rs y a ross edischareelpath is. prov ded with axp r l relatively. ar onenine's e rpine ph of the bottom portion- Adfiitionalsmalle f, con-ventionallfgridopenings areprovidedin sufficient number to, permit passage; ofthemak-imum required. curr nt. h v ar ene he loneninss permit. easy.startin fifthe' oondno nnyc erat thelow vapor pressures encounteredatlow tom-'- per'ature, starting without loss or control at higheroperating. temperatures. This advantage is" due to th proximity :of thea t ro gh" he peripheral'gridjopenings to the cond-ucting;wallv or.envelope surface, which quickly deionizes the nearby. aroplasma of thdischarge nathrthro sh the 1arge..pier pheral sr 'dlo ni ss h f a ondcti n cyc e-y uch" a sa fang men IIOtlaQYGESEIY- eiIect the maximumopera t perature and" the. 1-current'capacity; of th ow. va or pressu es c erodiwhere: low amb en temp. .v

The features which I desire to, protect arev pointed out wi h p t u a iy; amended. cl ims. The in n on' f t ge her safes} meta withfurther ob.ot and adv n a es tth iiinay e l wifij ,t h r win in .wn 'oh' i'e-j isnew al' V ew, or is h g8 d so iption taken i conn c n Wi deviceembodying my nvention; Fig; 2- is a hottom. view otithe .o trnl. e' Eroo n; Fi 1'; Big; .3. is a'uott n; v ewiof-i' g the rid.'emnoyedimFig-l1;. and. 51a tional' View off a portion of "anotherudisohargedevice/embodying my invention. j

Rei rrin now toi liis- I h hDW n Sichargle. device I embodyin in e io ontwo metal oylnidersz'and o spa d'f s j awator j cket between them,comprise an; 1%?- ated. conduc e env ope 'io idis harse dev ce- Inlet.andv outlet connections t r .oooling o are respectively plaooda the. botom'and the outer cyl nder a in ic ted; a 41am: sn oe b twe n. th nn r.and outer... cylind and. is c1Q$e.d..-at .the, endsofthe cy1ind).closure r s, 6 r. o her. suitable. meansn transverse header 8.

end of the envelope in contact with the lower This cathode may comprisea body of mercury or some other material, such as cadmium, which iscapable of analogous use. A cathode current terminal is provided by aterminal block l0, secured to the underside of the lower header 8. Astarting electrode II, which, as illustrated, is of the immersionignitortype, is insulatingly supported from the lower header. An externalterminal 52 for the starting electrode extends through the lower header8 and is insulated therefrom. A conventional holding anode I3 issimilarly insulatingly supported from the lower header with its externalterminal I4 extending therethrough.

-;Within the envelope at its upper end is an anode [5 in the form of agraphite cylinder mounted on a rod-like conducting stem It. A lead-inarrangementcomprising a flanged metal cylinder IT, a glass sleeve I8,and a metal cap [9 serves to insulatingly support the anode and its stemfrom the upper head 1. An anode terminal block 20 is secured to theupper surface of the metal cap I9 and ,a flexible copper cable 2! issuitablyconnected to the terminal block to serve as a means forconducting current to the anode.

,An apertured graphite control electrode or grid substantially surroundsthe anode [5 to thus extend across the path of any discharge are betweenthecathode 9 and the anode l5. This grid may suitably takethe form of abasket having a flat bottom 23 extending transversely of the cylindricalcasing and intersecting any straight-line path between the grid andanode. The grid is, of

course, insulated and spaced from the anode and the envelope in orderthat it may function as an electrostatic control electrode, but itsperiphery is relatively close to the envelope where deionizationtime isshortest. Ihe cylindrical side portion 24 or flange of the grid isintegral with the grid bottom 23 and is connected at its upper endto'the upper transverse header 7 by a plurality of'cylindricalinsulating bushings 25. A grid terminal bushing 26 is also connected tothe grid and extends through the upper header to provide an externalconnection for applying the grid potential.

A splash bafiie 2! is mounted above the cathode between the cathode andthe face of the anode to prevent any droplets of mercury from splashingonto the grid or anode. The bafiie may suitably take the form of a diskso positioned as to b ock any straight-line path between the activesurface of the cathode and the anode.

,As shown in Figs. 1 and 2, the grid is plurally I perforatedor'apertured to allow a .number of arcdischarge paths therethrough inorder that the initiation of the conduction cycle during each periodwhen the anode is positive with respect to-the cathode may becontrolledby the grid potential. In accordance with my invention and asfurthershown by Fig. 2 the bottom 23 ofthe gridielectrode is provided with aplurality of relatively large' openings, 28 near its periphery. Theseopenings may-suitably be circular perforations for ease of manufacture.Since the splash baffle. 21 blocks. any straight-line arc pathbetweenthe cathode and the anode, the shortest arc paths to the anodeextend around the edge of the baffle and through the large peripheralgridiopenings 28. Despite the relatively large size of the openings,however, arc-backs through theselarge grid openings are minimized due tothe proximity of the grid openings to the inner casing orenvelope 2,which eifects rapid deionization of the arc plasma after the conductionperiod. The deionization processis itself conventionalthe device-casing2 is at cathode potential so that it discharges the ions, and it servesto cool and condense the cathode vapor.

The advantage of the large grid openings 28 is realized at low vaporpressures when the mean free path of the ions is relatively long and thearc voltage needed to produce the required ionization in conventionaltubes is relatively high. Since the large openings minimize constrictionof the arc path by the grid the electrons initiating conduction are ableto pass through the grid openings in greater numbers to reach the anode.The cathode vapor is also able to difiuse more quickly into theregionbetween the anode and grid and thus replenish the available ionsupply. This advantage is especially significant in high current tubesof relatively large volume where the arc paths are longer. It has beenobserved that without the presence of the large peripheral grid openingsemployed according to my invention, the arc path may be so constrictedthat at extremely low vapor pressures there are insuflicient ions toneutralize the spacecharge and for an instant the current is abruptlyreduced as in a high vacuum discharge device with resultant voltagesurges produced in the associated circuit. I v I In larger deviceshaving greater volume and longer are paths, the necessity of preventingarc constriction increases and it is likely that a substantial thicknessof the grid face is required to provide mechanical strength andresistance to deterioration. Accordingly, the diameter of the peripheralgrid openings should also be keptrelatively large withrespect to thethickness of the grid, i. e.,the distance through it. This ratio shouldbein the neighborhood of 4:1 or'greater to permit most of the electronsto pass through i Were these center openings 29 also to be largeas theperipheral openings, arc-backs would more frequently occur at hightemperatures since the arc plasma in the center portions of thedischarge device requires a greater deionization time at the end of theconducting cycle due to its distance from the cooled conductive sidewall2.

In the embodiment of my invention shown in Figs. 1 and 2, I have alsoshown a plurality of grid openings 30 positioned between the centralopenings 29 and the largeperipheral openings 28, these intermediateopenings 30 also being intermediate in size. By utilizing such agraduation in size of the grid openings from the center of the gridbottom to its periphery to compensate roughly forthe deionization timeof'the arc plasma from the center of the discharge device to itssidewalls, the operating characteristics are further improved.

A plurality of grid openings 3| are also provided in the cylindricalsidewall of the grid to increase the short-circuit'capacity andalso topermit greater heat dissipation. from'thejanode mtnesieewans oretlieidevicer fI hese opnings are acent the sdewallsmfithestubeabutztheir size i'seiincreasing ss Eiinportant with-l the;crease in tli are-paths lirough than Accordinglwwhile flie size mf tlieopenings fil could he?- variously regulated fihave no't wand iti'necessary td db 7 so sinee gnc openings ifs th-b'o'ttom f aceiof meiifng ftowards thepenter-of the grid bottom so that greaterelectros-tatic--control rnay be eierted at this apex," while the largerand more open portion of the grid opening is nearest the periphery wherethe deionization time is less. Various configurations and combinationsof larger and smaller openings may be employed without departing fromthe spirit of my invention, depending upon the requirements of thedevice as to minimum vapor pressure and current requirements.

In Fig. 4, I have shown my invention as embodied in a single anode,multi-grid discharge device of the type having a pool-type cathode. Inthis device, the anode 35 is surrounded by a successive plurality ofgrids; in this case, an

inner grid 36, an intermediate grid 81, and an outer grid 38. Theenvelope 39 of the device is preferably a double-walled metalliccylinder of the type shown in Fig. 1 and which acts in the same mannerto deionize the arc plasma at the end of each conduction cycle. Each ofthe grids is provided with a plurality of central openings 40 whichoperate in a conventional manner. In accordance with -my invention, aplurality of larger peripheral or near peripheral openings 4|, whichfunction as to the large openings 28 shown and described for Figs. 1 and2, is provided in the bottom portion of each grid. While those portions"of the arc path defined by the large peripheral openings in the innerand intermediate grids 35 and 31 are not subject to such rapiddeionization as are the arc path portions at the peripheral openings inthe outer grid 38, the inner and intermediate peripheral grid openingsshould also be relatively large in order not to constrict the arc pathsand cancel the advantages obtained by utilizin the large peripheralopenings in the outer grid. The large peripheral openings in therespective grids are preferably aligned so far as practical to furtherdecrease arc constriction and permit electrons to reach the anode tobegin'each conduction cycle. Since without the large openings nearthegrid bottom peripheries the minimum vapor pressure at which conductioncould start would be relatively high, due to the constriction of the arcpaths caused by the plurality of grids, my invention is veryadvantageously employed in multi-grid devices of this nature.

For the purpose of this application, I have used the terms grid andcontrol electrode synonomously and intend that they be so interpreted. 1

While the present invention has been described by reference toparticular embodiments thereof, it will be understood that numerousmoi-22ers Iengtrsand; voltage fdi op 'required or Pats use arr withontactdally departingifromifthe he;

venticn I", therefore aintzzin the is'appended claims to covenal l' sucequivalentivariartl'onsms coins tr ue spirit an'eb scapes ofa-ithefbiegeri disclosurez wag claim as newi'andidesirezto lfletter si atentof 'til'e Unitedj s'tates =1.;Ain*. lectric 'diseharge iievice..comprisiirgr-ai single; 5m .1 anode and a. I pool-type 1 cathodetheanode -tofiprovid di'scharge paths fe conduction 'erebetweenmeans-lion dei6fli2ifig th$ spacei sai discharge ecure bya -c *a-cros'ssaid discharge; path with near said wall surfaces; caresses-seineprovided with a plurality of openings to define discharge pathstherethrough, said openings near the periphery of said surface beingsubstantially larger than those near its center in order to facilitateinitiation of conduction in paths near said deionizing means.

2., An electric discharge device comprising a single main anode and apool-type cathode spaced from the anode, deionizing means comprisingmetal wall surfaces laterallysurrounding the discharge path between theanode and the cathode, said metal wall surfaces being in conductiverelationship with said cathode, and

a control grid having a face extending transversely across saiddischarge path with its periphery near said wall surfaces, said face ofsaid grid having a plurality of perforations to provide arc passagestherethrough, the perforations near the periphery of said face beingsubstantially larger than the perforations near the center of said facein order to facilitate initiation of conduction in paths near saiddeionizing means.

3. An electric discharge device comprising a single main anode and apool-type cathode spaced from the anode, deionizing means comprisingmetal wall surfaces laterally surrounding the discharge path between theanode and the cathode, said metal wall surfaces being in conductiverelationship with said cathode, and a control grid having a faceextending transversely across said discharge path with its peripherynear said wall surfaces, said face of said grid having a plurality ofperforations to provide arc passages therethrough, the perforationsbeing progressively smaller from the periphery of said face to itscenter in order to facilitate initiation of conduction near saiddeionizing means.

4. An electric discharge device comprising a single main anode and apool-t pe cathode spaced from the anode, deionizing meanscomprisingmetal wall surfaces laterally surrounding the discharge pathbetween the anode and the cathode, said metal wall surfaces being inconductive relationship with said cathode, and a control grid. having aface extending transversely across said discharge path with itsperiphery near said wall surfaces, said face of said grid having aplurality of large openings near said periphery to provide arc passagesthere through, and relatively the center portion of said face beingimperforate in order to facilitate initiation of conduction near saiddeionizing means.

5. In an electric discharge device employing mercury as an ioniz'ablemedium and compri..-v ing a generally cylindrical elongated metalenvelopevgand an anodeqand cathode within the Y plurally perforateddisk-like graphite portion exenvelope at opposite ends thereof,a-.control electrode interposed in the discharge path between said anodeand said cathode, said electrode having a disk-liked portion extendingtransversely of said envelope withits periphery near said envelope, saidPortion having a plurality ;of apertures with at least one ofsaidapertures near its= periphery being substantially larger than coolingsaid envelope to facilitate deionization 20 2,500,153

of said space, and a control electrode having a tending transversely ofsaid discharge path'with 'its' periphery near saidzenvelope, saidportion having relatively large perforations near its periphery; thediameters of said perforations being at least four times the thicknessor said disk-like portion; and having substantially smaller;perforations near its center portion;

HARRY C. STEINER;

REFERENCES CITED The following references are of record in the file ofthis patent:- 'i' a i UNITED s'rAT s PA'I'ENTs v Date Number Name2,459,827 Marti- Jam 25, 1949 2,490,087 Pakala' Dec. 6, 1949 Cork Mar.14, 1950 2,501,308 i -Boyer Mar. 21, 1950

